refactor(reddit): migrate to http.get(params=...) helper

Added params kwarg to http.request()/http.get() that urlencodes a dict
into the query string. None values are dropped, ints and bools are
stringified, and params append correctly if the URL already has a
query string.

Migrated reddit.py to use this helper for all three ScrapeCreators
call sites (global search, subreddit search, post comments). Deleted
the try/import requests/except ImportError fallback and the paired
if not _requests: / else: branches. Six new http tests cover the
params-encoding behavior.

Net: reddit.py -70 lines. Behavior is identical - the existing http.py
urllib implementation already had retry logic, 429 handling, and
HTTPError types that are strictly better than the ad-hoc requests
branches we deleted.

99 reddit tests pass. Live smoke test on a real ScrapeCreators run
returned 12 threads with the same engagement data as before.

scripts/lib/http.py

@@ -38,6 +38,7 @@ def request(
     url: str,
     headers: Optional[Dict[str, str]] = None,
     json_data: Optional[Dict[str, Any]] = None,
+    params: Optional[Dict[str, Any]] = None,
     timeout: int = DEFAULT_TIMEOUT,
     retries: int = MAX_RETRIES,
     max_429_retries: int = MAX_429_RETRIES,
@@ -50,6 +51,8 @@ def request(
         url: Request URL
         headers: Optional headers dict
         json_data: Optional JSON body (for POST)
+        params: Optional query-string params. Values are stringified. None values
+            are dropped. If ``url`` already has a query string, ``params`` is appended.
         timeout: Request timeout in seconds
         retries: Number of retries on failure
         max_429_retries: Maximum 429 retries before giving up (separate cap)
@@ -64,6 +67,12 @@ def request(
     headers = headers or {}
     headers.setdefault("User-Agent", USER_AGENT)
 
+    if params:
+        filtered = {k: str(v) for k, v in params.items() if v is not None}
+        if filtered:
+            separator = "&" if ("?" in url) else "?"
+            url = f"{url}{separator}{urlencode(filtered)}"
+
     data = None
     if json_data is not None:
         data = json.dumps(json_data).encode('utf-8')